Flue-gas-recirculation system for shell stills



Oct. 28, 1930. ATWATER 1,779,405

FLUE GAS RECIRCULA'PION SYSTEM FOR SHELL STILLS Filed Feb. 16, 1928 2Sheets-Sheet l (r -Tw- /0 50 i: w I

INVENTOR BY Harry 14.19

M QQUQJ ATTORNE Oct. 28, 1930. H. A. ATWATER 1,779,405

FLUE GAS RECIRCULATION SYSTEM FOR SHELL STILLS Filed Feb. 16, 1928 2Sheets-Sheet 2 ATTORNEI} Patentecl' Oct. 28, 19

UNITED'STATES HARRY A; ATWATER, or' xans'ns CITY, MIssoURrFLUE-GAS-RECIRCULATION SYSTEM FOR SHELL STILLS Application filedFebruary 16,1928. Serial m.-254,79a.

The present invention relates to oil refining apparatus, andparticularly torefining or toppingstills of the shell type, and aims toimprove the efficiency of such apparatus c by providingffor therecirculationof a 'portion of the flue gases in suchwa manner as to notonly increase the area of the'heat exchange surfaces but also therefining capacity of apparatus of this type. It is also sought to devisea still construc tion of this character in which this increasedefficiency is efiected along with an increase in fuel-economy due to therecirculation feature, and'at the same time the danger'o'f'injury to thestill structureon account of socalled.hot spots is practicallyeliminated.

- In carrying out theseobjects of the invention, it is further sought toprovide apparatus of such character as to improve gen- 2 erally shelllstill constructions. for which the invention is especially. adapted.

With the foregoing general objects in view, the invention will now bedescribed by reference-to the accompanying drawings il- M lustrating oneform of furnace and shell still construction which is adapted forthe embodiment of my improvements, afterwhich those'features and combinationsdeemed to be novel will be set forthand claimed.

In the drawings 1 i -.:Figure 1 is a plan view; showing a portion of astillbattery embodying the herein de-V scribedflue gas-recirculatingsystem; 7 c

Figure 2 is a side-elevation, partly broken away :and in verticalsection; J

- Figures 3 and 4 are views inrear and front elevation, respectively; lFigure 5 is, an enlarged: detail view illusi V a .t

Figuresi6 and 7 are end views of one of the recirculating flues, showingtwodifierflow of flue gas.' I c In the drawings .is illustrated a commonform of shell stillunit 10,.usually'arranged ent forms of ribs orfinsfor dividing the in battery form with "each unit 10 overlying :a"furnace or combustion. chamber '11 using either a'solid fuel, .or oil orgas, as in the illustrated apparatus, this fuel being trating' theinterior ofone of the recirculatsupplied-by way of aburner opening '12.lhe'air for supporting combustion in the illustrated construction isadmitted through an intake opening 14 into a bottom chamber 15,, andthence through checker openings 16 into the combustionchamber 11, fromwhichv the waste flue gases are conducted outv through a furnace fluepassage 17 to a tunnel 18, and thence to a stack (not shown),

WVhere a series of suchstills are operated asa continuous'battery,.thosestill units in which the finalfractions aretaken oiffrom thecrude oilmust be operated at a comparatively high temperature, resulting in fluegas temperatures of around nine hundred degrees Fahrenheit whereas, inthe stills at spotswhich alwaysfollow rapidly the-ace V cumulation or"deposit of carbon, at low temperature nact the battery especially; Butthls excess air must beheated, and hence the i excessiv'efiring and fuelconsumption for'tha-t purposeat low temperature end of 1 the batteryEven so, the firing can only be carried on within certain limits,because of this dangerof hot spots, and such limitation infiringtemperature likewise limits the ca-i pacity of the? still. I

These inefficient characteristics inherent in the operation of shellstills have long been 'recognized andrhave resulted in the gradualabandonment of this type in favor of the more efficient tube still,wherever new installations n a are being made .However, a vast number'of shell still installations are yet being opoperated, as theyrepresent an enormous investment, too great either to abandon or! toconvertiover into thetube form of still. It isthe purpose 'of thepresent inventionzto r' surface alone.

render these shell types of installations very much more elficient, andthis I have found to be possible by the simple expedient of substituting for the excess air employed in the combustion chamber acertain amount of recirculated flue gases, for the reason that therecirculation of such gases is practicable and feasible Where provisioncan be made to efr feet a greater percentage of heat transfer from thecombustion gases to the contents of the still by convection or rubbingcontact with the heat exchange surfaces than ordinarily takes place inthe usual shell still construction through the medium of its bottom Ifthe necessary additional heat exchange surface can be incorporated intothis old shell type, and a further safety factor introduced for.blanketing and temperingthe hot combustion gases directly be neath thestill bottom, it Will beunderstood that the results sought after in thisconnection may be accomplished.

lVith this end in view, each flue passage 17 is provided with a gatedamper 20, and at some point along the flue gas tunnel 18 connection ismade for each battery, as by a.

bendio'r elbow 22, with a suction fan 2 f for pullingia certain volumeof the hot flue gases.

from the tunnel 18 and discharging the same into a header conduit 26, asclearly. shown in Figures 1 to 3. From the header 26 connection is madeby means ofibranchconduits ori pipes 28 with a series ofuflue pipes 30,preferably two pairs of such flue pipes for each still unit 10, thesefiues 30 extending longitudinally through the still, and at points notinterfering with the manholes 31 and at some distance above the bottomof the still so as to afford access thereto for cleaning purposes. Atthe front end of each still, return bends 32 are connected with the endsof the flue pipes 30 for reconducting the fiuegases to the combustionchamber 11 into which the recirculated gasis discharged through a passsage 34 located near the top ofthe chamber 11 and above the peephole 35usually provided at the front of the furnace.

A suitable damper 36 is provided in the elbow 22 of each battery, and adamper 37 is located in. each of the branch pipes 28, for facilitatingthe proper regulation of the flow of the gases; and a cable 38 andsuitable coun-' terwcight 39 may also be provided for facilitating theregulation of each of the dampers 20 above referred to (see Figure lVithsuch an arrangement, it willbe seen that each still unit has a damperedcommunication with the flue gas passages 1718, and by control of thedampers the flue gasescan be recirculated through .any one or more ofthe still units at will, and the extent or volnine of the flowconveniently regulated to any desired degree.

On account of the length of the stills,rang-. ing from thirty tofortyfeet, thetubes 30 will ordinarily be of comparatively large diameter, orfrom six to twelve inches, hence with flues of this size, without otherprovision, there would probably be a loss in efiiciency of heat transferon account of the large core of gases traveling axially through the finewithout coming in-contact with the interior surfacethereof; I thereforecontemplate using ahollowhcore tube 40 (Figure 5) closed at each end bythe preferably tapered terminals 41, each core tube being of smallerdiameter than the flue, whereby the recirculated flue gases are causedto travel through the annular space between ,the flue and its core. Eachcore is maintained properly spaced centrally within the flue by means oflongitudinal ribs or fins 42- (Figure 6). by which the flow of gases is.split or divided, and. these may be obliged to follow a still longercourse through the flue by substituting ribs or fins of helical outlineasillustrated at LE/in Figure 7.

By means of the above described recirculatingv arrangement, it will beseen that the flue gases which are returned to the combustion chamber11through the passages 34 are utilized in place of the excess airordinarily used, and sincethese gases are still relatively iot their userepresentsa clear gain in fuel economy as represented by the differencein temperature of such gasesand that of the atmospheric air it replaces.The discharge of the iecirculatedgases into the upper portion of thecombustion chamber produces a tempering orblanketing eifectiupon thecombustion gases, and thus protects the bottom of the still to such anextent as to practically eliminate .the dangerof. hotv spots, and therate offiring can be increased without danger to the still bottom. Thisincreased firing rate is ,ofcourse desirablein the interest of greaterstill capacity, and. furthermore is made practicable and feasible by theincreased heat transferring 1 capacity afforded by the convective:heating surface. of the flues 30. Ihe displacement of excess air by therecirculated flue gases also works outin the interest of increasedfiring rate because of the higher percentage of CO in the freshcombustion gases and resultant highervfiame temperatures. amount ofheatevolved is ofisetby the increase in the rate of heat transferthrough the medium .ofthe flues 30. and the extensive area of convectiveheating surfaces there provided, this means an increase instill capacitywhichdoes not impose any increased or excess burden upon the bottomheating surface of the still;

An additional advantage in theimproved construction resides in itsadaptability to continuous battery, stills in, rerun'operations, inwhich the necessity of direct firing can be dispensed with in connectionwith thoseunits whichare fired only. very lightly, since the fairly hotrecirculated.fluegases will afford But as. the increase. in the,

the requisite heating capacity in lieu of such direct firing. This is adistinct economical gain, especially since it is well known that directfiring is always a comparatively inefficient process where the rateoffiringhas to be kept low. The selective regulation provided in theapparatus herein described not only makes such indirect firing operationpossible, but permits such convenient adjustment of the operation of thedifferent stills of the same battery as may be desirable. Again Wherethe particular stills of the same battery all require to be fired at thesame rate, the increase in the heat transfer capacity by means of theflue structure herein described makes possible a lower firing rate forthe same still capacity, or if the former firing rate be maintained thestill capacity will be increased; hence, if the former rate of firing isinjurious to the still, the improved flue gas recirculating system willprovide the.

means for eliminating such injury Without any loss of capacity.

It Will thus be apparent that I have devised a practical and efiicientarrangement and construction for fulfilling all the desired objects ofthe invention, and it is equally apparent that the construction orarrangement of the system can be altered in any desired or required wayto meet varying conditions of operation, and is in no sense tobe limitedto details herein illustrated; accordingly, I desire to reserve theright to make all such changes or modifications as may fairly fallwithinthe scope of the appended claims.

Having thus described my invention, what I claim and desire to secure byLetters Patent 1s 1. Flue gas recirculating apparatus for oil refiningshell stills comprising, in combination with a furnace combustionchamber and an oil refining still of the tubeless shell type typeoverlying said chamber, one or more flues extending through saidstill,and means for conducting a portion'o-f the waste flue gases from thecombustion chamber, through said fines and thereafter discharging thesame into the space Within said combustion chamber directly underlyingthe bottom of the still. i V

3. Flue gas recirculating apparatus for oil refining shell stillscomprising, in combibers, a flue gas header provided with means fordiverting a portion of the combustion gases issuing fromsaid chambers,one or more fiues extending from said header through each of saidstills, means communicating with said fines for reconducting gases fromsaid flues to the combustlon chambers, and damper means for selectivelyregulating the recirculating flow of said gases through the 4;. Flue gasrecirculating apparatus for oil 'r efiningshell stills comprising, incombination with the combustion chamber and a still overlying sa1dchamber, a tube extending through the still, a core structure in saidtube and forming an annular passage there H through, and means forconductlng a portion of the Waste combustion flue gases from thecombustion chamber into said flue passage and thence back into thecombustion chamber.

5. Flue gas recirculating apparatus for oil refining shell stillscomprising, in combination With the combustion chamber and a stilloverlying said chamber, a tube extending through the still, a coreextendlng axially nature.

HARRY A. A'IWVATER,

nation with a series of furnace combustion chambers, an oil refiningstill of the tubeless shell type overlying each of said cham-

